Reuber H35 hepatoma cells in culture will be used to assay for glucocorticoid antagonizing factor (GAF). The assay is based on the ability of GAF to inhibit the glucocorticoid induction of phosphoenolpyruvate carboxykinase in these cells. The purification of GAF in serum of mice primed with zymosan in order to maximize the yield will be attempted through the appropriate application of column chromatography, ion exchange resins, gel filtration and isoelectric focusing techniques. Progress made up to the present time gives promise of success. Once the factor is obtained in pure form its properties will be compared with those of other mediators released by cells of the reticuloendothelial system in response to endotoxin. It will also be injected into rabbits and the antiserum that develops it will be employed in assessing more precisely the role played by GAF in endotoxemic animals.